C(O[CH2:9][CH3:10])(=O)C(OCC)=O.[O-][CH2:12]C.[K+].[CH3:15][C:16]1[C:21]([N+:22]([O-:24])=[O:23])=[CH:20]C(C)=C[C:17]=1[C:26](=[NH:30])OCC>CN(C=O)C.CS(C)=O>[CH3:12][C:10]1[CH:9]=[C:15]2[C:16]([CH:17]=[CH:26][NH:30]2)=[C:21]([N+:22]([O-:24])=[O:23])[CH:20]=1A solution of 2,5-dimethyl-3-nitroaniline from Step A (1.21 g, 7.26 mmol) and p-toluenesulfonic acid monohydrate (2 mg, 0.011 mmol) in freshly distilled triethyl orthoformate (1.65 mL, 9.92 mmol) was heated at 120° C. for 45 min in a distillation apparatus, and about 0.4 mL of EtOH distilled over. Vacuum distillation of the residual solution yielded ethyl 2,5-dimethyl-3-nitrophenylimidoformate (b.p.=146° C., ca. 2 mm Hg) as a pale yellow solid. To a solution of diethyl oxalate (868 mg, 5.94 mmol) in DMF (2 mL), at 0° C., was added potassium ethoxide (435 mg, 5.17 mmol) and the resulting solution was added to a solution of ethyl 2,5-dimethyl-3-nitrophenylimidoformate (880 mg, 3.96 mmol) in DMSO (3 mL). The reaction mixture was heated at 40° C. for 1 h than quenched with H2O (30 mL) and extracted with EtOAc (2×50 mL). The combined organic layers were washed with brine, then dried over Na2SO4, filtered, and concentrated in vacuo. The crude product was purified by silica gel chromatography, eluting with a gradient of hexane:EtOAc—100:0 to 0:100, to give the title compound. MS: m/z=177 (M+1).
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